"In the past 24 hours, I have developed mild symptoms and tested positive for coronavirus," said the conservative leader on the recording.
Johnson, whose romantic partner, Carrie Symonds, is pregnant, added that although she has "isolated herself", she will continue "leading the government's video conference response" against the pandemic.
"I can continue, thanks to the magic of modern technology, communicating with my team to lead the national fight against the coronavirus," said Johnson, who thanked the "wonderful staff" of the National Health Service.
The latest Covid-19 data from the U.K, as of 17:00 on March 25th is:
People tested: 104,866 (+7,847)
Confirmed cases: 11,658 (+2,129)
Confirmed deaths: 578 (+115)
Rate of change of deaths: 25% (+15%) 5 day moving average: 20% (-1%)